The invention relates to a rotary piston machine with rotors enclosed in a common casing and rotatable about fixed shafts, surfaces of the outer circumference of at least one of the rotors performing their rotary movement about one of the shafts with sealing gap-forming spacing along at least one cylindrical inner surface of the casing.
The efficiency of such machines, e.g. in compressing a gaseous medium, is largely determined by the quality of the seal of the rotors with respect to the surrounding casing. In order to obtain narrow sealing gaps, the casing, the rotors and their bearings must be manufactured and assembled with high precision, which leads to correspondingly high manufacturing costs.
A further complicating factor is that under the influence of centrifugal force and the operating temperature, the rotors assume a larger diameter and the casing suffers from thermal distortion.
The prior art sealing gap dimensioning was directed, in the case of maximum speed and the least favourable temperature distribution, at leaving a residual gap at all points such as is necessary in order to reliably prevent any risk of large-surface contact and the resulting seizing of the rotors at the high speeds which occur of e.g. 40 m/s and higher.
The very considerable difficulties in on the one hand determining and taking account of size changes or distortions and on the other hand the need for a residual gap under all conditions, have led to sealing gaps, which are wider than are absolutely necessary.
The problem of the invention, in connection with a machine of the aforementioned type, is to so improve the sealing of the circumferential surface of a rotor with respect to the casing inner surface, that the machine can be manufactured with relatively limited costs, that the minimum sealing gap width is obtained and that the risk of the rotor seizing is eliminated.